Air circuit breakers as described within U.S. Pat. Nos. 3,095,489 entitled "Manual Charging Means for Stored Energy Closing Mechanisms of Electric Circuit Breakers" and 3,084,238 entitled "Ratchet Mechanism for Charging a Closing Spring in an Electric Circuit Breaker" include operating mechanisms that are mainly exposed to the environment. Since the air circuit breakers are rated to carry several thousand amperes of current continuously, the exposure to convection cooling air assists in keeping the operating components within reasonable temperature limits.
Such air circuit breakers are usually provided with a motor operator such as described in U.S. Pat. No. 4,167,988 entitled "Ratcheting Mechanism for Circuit Breaker Motor Operator" or a manual handle as described in U.S. Pat. No. 3,729,065 entitled "Means for Charging A Stored Energy Circuit Breaker Closing Device" for charging the powerful closing springs contained within the air circuit breaker operating mechanism.
When the circuit breaker closing springs are brought to their fully-charged conditions, it is important that the springs do not become inadvertently discharged while an operator has hold of the charging handle in order to avoid damage to the ratchet mechanism and the associated air circuit breaker contacts. An early arrangement of a latching means to prevent rotation of a closing springs charging handle is found in U.S. Pat. No. 4,475,021 entitled "Air Circuit Breaker".
When the circuit breaker closing springs are completely charged, the holding pawl is removed from the charging gear to allow the charging shaft to rotate in the reverse direction when the circuit breaker closing button is activated, as described in U.S. patent application Ser. No. 08/863,649 entitled "Ratcheting Mechanism for an Industrial-Related Circuit Breaker".
The above-noted U.S. patents and U.S. patent application include means for opening and closing the circuit breaker contacts by direct access to the circuit breaker as well as from a remote location. To prevent closing the circuit breaker contacts when the associated electric equipment is undergoing replacement or repair, interlocks are required. U.S. Pat. No. 5,504,285 entitled "Circuit Breaker Indicating Flag Interlock Arrangement Operating Springs" and U.S. Pat. No. 5,478,979 entitled "Circuit Breaker Closing and Opening Interlock Assembly" provide interlock arrangements acting between the circuit breaker ON and OFF buttons to prevent inadvertent turn on of so called "insulated case" circuit breakers wherein the circuit breaker operating components are completely contained within a common enclosure.
It is known that circuit breaker contacts can become welded closed upon repeated intense overcurrent occurrence, especially when the circuit breaker is used within circuits that occasionally carry circuit current in excess of the circuit breaker ratings.
When multipole circuit breakers such as described in the aforementioned U.S. Pat. Nos. 3,084,238 and 3,905,489 incur one set of welded contacts while the remainder of the contacts within the separate poles remain operational, it is helpful to identify which of the contacts have become welded.